Created
July 17, 2021 14:19
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credit to parkershamblin
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class ListNode: | |
def __init__(self, val): | |
self.val = val | |
self.next = None | |
class LinkedList(object): | |
def __init__(self): | |
""" | |
Initialize your data structure here. | |
""" | |
self.head = None | |
self.size = 0 | |
def get(self, index: int) -> int: | |
""" | |
Get the value of the index-th node in the linked list. If the index is invalid, return -1. | |
""" | |
if index < 0 or index >= self.size: | |
return -1 | |
current = self.head | |
for _ in range(0, index): | |
current = current.next | |
return current.val | |
def addAtHead(self, val: int) -> None: | |
""" | |
Add a node of value val before the first element of the linked list. After the insertion, the new node will be | |
the first node of the linked list. | |
""" | |
self.addAtIndex(0, val) | |
def addAtTail(self, val: int) -> None: | |
""" | |
Append a node of value val to the last element of the linked list. | |
""" | |
self.addAtIndex(self.size, val) | |
def addAtIndex(self, index: int, val: int) -> None: | |
""" | |
Add a node of value val before the index-th node in the linked list. If index equals to the length of linked | |
list, the node will be appended to the end of linked list. If index is greater than the length, the node will not | |
be inserted. | |
""" | |
if index > self.size: | |
return | |
current = self.head | |
new_node = ListNode(val) | |
if index <= 0: | |
new_node.next = current | |
self.head = new_node | |
else: | |
for _ in range(index - 1): | |
current = current.next | |
new_node.next = current.next | |
current.next = new_node | |
self.size += 1 | |
def deleteAtIndex(self, index: int) -> None: | |
""" | |
Delete the index-th node in the linked list, if the index is valid. | |
""" | |
if index < 0 or index >= self.size: | |
return | |
current = self.head | |
if index == 0: | |
self.head = self.head.next | |
else: | |
for _ in range(0, index - 1): | |
current = current.next | |
current.next = current.next.next | |
self.size -= 1 |
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